Top Democrats in charge of keeping the Senate in Dem hands and maintaining the political health of the party — DSCC chair Patty Murray and messaging chief Chuck Schumer — have privately expressed frustration that deep Medicare cuts risk squandering the major political advantage Democrats have built up on the issue, people familiar with internal discussions say.

Senators Murray and Schumer, along with other Dems like Debbie Stabenow and Mark Begich, have warned against deep cuts in recent leadership meetings, a source familiar with the meetings says, another sign of the unrest that the possibility of serious entitlements cuts is creating among Congressional Democrats.

“We shouldn’t be giving away our advantage on Medicare,” said a source familiar with Murray’s thinking, in characterizing her objections in private meetings. “We should be very careful about giving away the biggest advantage we've had as Democrats in some time.”

“For the first time in the past two and a half years we have an unmitigated advantage on a single issue where our entire caucus is united,” the source continues. “This is a case where the whole morale of our party was lifted by the fact that we were taking the fight to Republicans.”

The frustration on the Senate side is mirrored on the House side. Sam Stein reported on Friday that DCCC chair Steve Israel privately vented his frustration that serious Medicare cuts would hamper his ability to recruit good Dem candidates to challenge House GOP incumbents. And a number of Dem challengers have already launched their campaigns by alluding to the GOP’s unpopular Medicare plan, a reminder of just how central top Dem strategists want it to remain through 2012.

In red states like Montana, Nebraska, and Missouri, one key to good Dem performance is maintaining good standing among seniors. The Dems took a shellacking in 2010 in part because of the swing in seniors in such states. One measure of this is that Ben Nelson, a conservative Dem who opposes tax hikes as part of any deficit deal, has also come out against any cuts to Social Security and Medicare.

“Schumer has consistently expressed the most concern,” a source familiar with recent leadership meetings says. “Schumer has been on this bandwagon for weeks.” The source adds that a recent meeting at which Stabenow and Begich sounded the alarm about cuts ”got pretty heated.”

Concludes the source: “There’s a high degree of frustration within the caucus.”